Field of the Invention
The present invention relates to, a light source unit including a collimator lens, and a projector including the light source unit.
Description of the Related Art
In these days, data projectors are used on many occasions as an image projection system which projects an image of a screen or a video image of a personal computer, as well as images based on image data which is stored on a memory card or the like on to a screen. Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made many proposals of projectors using laser diodes which can save electric power, which have long service life and which are highly bright.
A projector disclosed in the Japanese Unexamined Patent Publication No. 2013-190591 includes as light sources a blue laser emitter which emits light in the blue wavelength range, a red laser emitter which emits light in the red wavelength range, and a luminescent light emitting device which emits light in the green wavelength range as a result of excitation light being shone on to a luminescent material layer thereof. Laser rays emitted from the laser emitters are shone on to a microlens array via collimator lenses, whereby the laser rays are guided to a display device as diffuse light rays of a uniform light intensity distribution. Similarly, the luminescent light from the luminescent light emitting device is also guided to the display device via the same microlens array.
It is known that light emitted from a laser diode takes an elliptic cross-sectional shape. The Japanese Unexamined Utility Model Publication No. 5-45656 discloses a light source unit in which a cross-sectional shape of light emitted from a laser diode and collimated by a collimator lens is shaped into a circular shape through the use of two cylindrical lenses whose axial directions are made to coincide with each other.
In the projector disclosed in the Japanese Unexamined Patent Publication No. 2013-190591, the light emitted from the laser diode and the luminescent light from the luminescent light emitting device pass through the same microlens array. In general, light emitted from a laser diode has strong directionality and is shone over a narrow range.
Because of this, when a laser ray is incident on a microlens array which is adjusted to an incident range of light in the green wavelength range which is luminescent light, the laser ray is shone on to a small number of microlenses, which sometimes results in a case where the intensity is not uniformed sufficiently.
When small microlenses are used for such a microlens array in order to enhance the uniformity in intensity distribution of a laser ray, the loss of transmitted light is increased by connecting portions where the small microlenses are connected to one another, resulting in a reduction in light utilization efficiency.
On the other hand, when the number of microlenses through which a laser ray passes is attempted to be increased by expanding the shining range of the laser ray with a collimator lens, the collimator lens needs to take in portions of the laser ray which expand along a major axis of the elliptic cross-sectional shape, and therefore, a large collimator lens needs to be used, which eventually calls for an enlargement in size of the projector.
In addition, even though an application does not require a laser ray to be circular in cross section at an exit surface of the collimator lens or an application does not require that the laser lay is collimated accurately, in case an angle of emission of the laser ray is not uniform with respect to an optical axis of a collimator lens (namely, the laser ray is expanded in a elliptic shape), there may occur an unfavorable case for a post utilization of the laser ray.